This project proposes to examine systematically various regions of the rat brain not only to locate those areas involved in prolactin secretion but also identify the biogenic amines. To undertake this study ovariectomized female rats will have a catheter placed into the aortic arch for serial blood sampling. A long acting estradiol preparation will be administered to produce a high and constant level of prolactin in circulation. Bilateral cannula will be implanted into various regions of the brain for microinjections. Brain regions to be examined will be the arcuate-ventromedial nuclei, paraventricular nuclei, preoptic and suprachiasmatic hypothalamic areas. Subsequent to examination of these areas, and if time permits, the amygdala and olfactory complexes will be studied. The study of a brain region will include the injection of neural antagonists and agonist with and without an ether stress. In this way an evaluation of both the basal and acute secretion of prolactin will be examined. Some neural antagonists studied will be atropine (cholinergic), phenoxybenzamine (alpha adrenergic), propranolol (beta adrenergic) and p-chlorophenylalanine (serotonergic); neural agonists will be acetylcholine, norepinephrine, dopamine, and serotonin. Within a single area neural antagonists will be injected first individually and then in various combinations. Serum samples will be taken before injection of the drug and 15, 30, 60 and 120 minutes after injection. Individual rats will be sampled approximately twice weekly and injected with a different drug or drug combination. Using a chronic rat in this manner minimizes the variability due to cannula placement. The prolactin concentration of the serum will be determined by radioimmunoassay. When an antagonist is found that alters prolactin secretion its agonist will be administered to determine if the opposite response occurs. In this way neural regions previously implicated in prolactin regulation by lesion and stimulation studies will be systematically studied for the biogenic amines involved in the regulation of prolactin.